Hydraulic power control device

ABSTRACT

The hydraulic power control device comprises a boost piston whose movements depend on the pressure of fluid contained in an actuating chamber, said pressure being controlled by a distributing valve connected to a pressure fluid source and to a reservoir. The valve is operated by a push rod through the intermediary of a lever connected to a double sensor responsive to the relative movement of the valve and of the boost piston. The lever presents a first end on which the sensor is pivoted and a second end pivotably secured to a sliding pin mounted in housing of the control device.

United States Patent [1-9] Carre 1 Dec. 24, 1974 [5 4] HYDRAULIC POWERCONTROL DEVICE 3,610,102 /1971 Brown, Jr 91/391 R Inventor: Jean-JacquesCarre, Montreuil,

France Primary Examiner-Paul E. Maslousky Attorney, Agent, or Firml(enC. Decker; William N. [73] Assignee: Socrete Anonyme D.B.A. Antonis [22]Filed: May 25,1973 [21] Appl. No.: 364,400 [57] ABSTRACT A The hydraulicpower control device comprises a boost 30] Foreign Application PriorityData a Whqse dmOvememS q g the of u1 contame in an actuating c am er,sat pressure June 12, France controlled a distributing valve Connectedto a pressure fluid source and to a reservoir. The valve is [g]91/384,F9;l5/l399l.1l3 Operated by a push rod through the intermediaryof a d A lever connected to a double sensor responsive to the 1 o earcrelative movement of the valve and of the boost pis- 56 R f Ct d ton.The lever'presents a first end on whlch the sensor 1 e erences ispivoted and a second end pivotably secured to a UNITED STATES. PATENTS vv v sliding pin mounted inhousing of the'control device. 2,976,8493/1961 Stelzer 91/384 3,047,341 7/1962 Alfieri 91/384 5 Clams 1 DrawmgFlgure 10a 11b [36 [old l 27 6 r 8/} /J--4 y 1 Y I I 1 A EM J I I 1 w ll 18' 3'5 0 52:2 50 1 I w, 7 i M 20 4 Mid 44 2 28 w m v X t PATENTEB DEC2 41974 aw is HYDRAULIC POWER CONTROL DEVICE side a body a servo pistonwhose movements depend on the pressure of fluid contained in anactuating chamber, the said pressure being controlled by a distributingvalve connected to a pressure fluid source and to a reservoir, the valvebeing movable by means of a follower mechanism which acts under theinfluence of the servo piston andof a push rod capable of moving theservo piston directly in the event of a pressure failure in theactuating chamber.

In a servomotor of this type, the stroke ratio of the input push rod andof the servo piston, which is normally connected to a conventionalmaster-cylinder, is constant and equal to unity during normal assistedoperation min the event of an accidental failure. It is thereforeimpossible for the designer to reduce the effective stroke of the pushrod as desired by users, without making operation of the vehicle brakesextremely difficult in the event of failure of assisted braking.

According to the invention, the follower mechanism comprises a doublesensor, cooperating with the servo piston and valve, and a lever onwhose first end the sensor is pivoted and whose second end is pivotablymounted relative to the body, the pushrod being arranged in the body soas to act on the lever by way of a bearing point situated between thetwo points at which the lever is pivoted relative to the sensor and tothe body.

According to a preferred embodiment of the invention the second end ofthe lever is pivoted on a pin slidable relative to the body andresiliently urged into an idle position fixed relative to the body. Thestructure prevents any deterioration in the follower mechanism in theevent of a failure of assisted braking, for example due to jamming ofthe distributing valve in its housing.

According to a further feature of said preferred embodiment, the supplychannel connecting the distributing valve to the actuating chamber iscontrolled by a valve attached to the pin in such a way that the lattervalve is urged into its closing position as soon as the pin is moved outof its idle position. This feature prevents an abrupt return of pressurefluid to the actuating chamber when the distributing valve comesfree-again.

The invention will now be described by way of example with reference tothe accompanying drawing, in which:

' The single FIGURE represents a longitudinal section through aservomotor and distributing valve which embody the invention and whichare'used in a motor vehicle brake circuit.

(not shown) and it communicates with-a first brake circuit through anoutlet 26. A return spring 27 urges the piston into the positionillustrated in the 'FlGURE. Persons skilled in the art will readilyappreciate that the combination of the bore 14, piston 18 andreplenishing valve 24 constitutes a conventional, well-known brakemaster-cylinder. which will not be described in detail.

The piston 18 contains a cavity 28 which gives on to the actuatingchamber, and into which the inner end 32 of a push rod 30 projects. Thepush rod 30 can slide through the cover 16 in a fluid-tight manner, andin the embodiment illustrated it is coaxial with the piston l8.

The push rod is connected in conventional fashion to the brake pedal ofthe vehicle. A radial annular extension 34 of the push rod'can bear onthe cover to define the idle position of the rod 30 and piston 18.

A damper pad 36 of elastomeric material is arranged as illustratedbetween the bottom of the cavity 28 and the end 32 of the push rod.

The body contains a bore 38 connecting the two bores 12, 14. When thepiston is in its idle position, the bore 38 leads into the bore 14between two sealing collars 40, 42on the piston 18. An annular space 44between the collars 40, 42 is connected to the cavity 28 by a pluralityof ports 46. Accordingtofa variant of the invention a seal may beprovided oneach collar.

Part of the end 32 contains a helical groove 50 coaxial with the longaxis of the push rod 30. As the FIG- URE shows, the edges of this slotare in contact with the surface of a cylindrical bore 52 formed in theend of the piston 18 and communicating with the cavity 28. The cut-offportion 50 of the push rod and the surface 52 in the piston 18 togetherdefine a narrow passage along which fluid can pass between the cavity 28and the actuating chamber 22.

The supply of pressure fluid is by way of adistributing valve mounted inthe bore 12.'Th'e valve comprises a movable assembly 54 slidable in atubular sheath 56 which is inside the bore 12 and which is fixed to thebody 10. The provision of the sheath 56 between the movable assembly andthe bore makes it possible to use appropriatematerials for thesecomponents and facilitates machining of them, which is difficult due tothe strict manufacturing tolerances.

The movable assembly 54 consists of a slider, comprising two annularbearing members 58, 60 connected by a spacer 62, and of a valve sleeve64 mounted between the bearing members 58, 60. As the FIGURE shows, thesleeve, which is shorter than the gap between the bearing members 58, 60and which can therefore move relative to the slider, is biased to abutaxially on the bearing member 58 by a prestressed sheath 56. It shouldbe noted that enough space is left between the inside surface of thesleeve 64 and the spacer to enable fluid to flow freely through thesleeve.

The spacer 62 is a tube on to which the bearing members 58, 60 arecrimped. The passage 72 inside the tube permits communication betweenthe actuating chamber 22 and the closed portion 74 of the bore 66. Be-

cause of this latter feature the slider is completely balanced inrespect of the pressures to which it may be subjected. g

A spring 76 bearing on the body urges the slider into the idle positionshown in the FIGURE, in which it bears on intake controlling means whichforms part of a connecting mechanism 78 (described below). Taking thebody as a fixed reference, the resilient forces of the two springsareopposite relative to the body.

The sheath 56 is also provided with two annular spaces 82, 84 connectedrespectively by an outlet 86 and an inlet 88 to a reservoir (not shown)and to a pressure fluid source (not shown), for example an accumulatorfilled by a hydraulic pump driven by the vehicles engine. The spaces 82,84 communicate with the supply chamber 68 by way of ports 90, 92provided inthe sheath 56. The length of the valve sleeve is such that itcan cover the two ports very precisely. When the sleeve is in its idleposition, as shown in the FIGURE, slight leakage is permitted betweenthe supply chamber 68 and outlet 86. To this end the bearing member 58contains radial slots 94 enabling fluid to flow between the supplychamber 68 and'port 90.

Finally, the sheath 56 is provided with seals on its exterior so thatthe various parts of the corresponding hydraulic circuit can be suitablyisolated, as illustrated. Furthermore the bore 38 is closed with a plug96, illustrated diagrammatically in the FIGURE.

The connecting mechanism 78, which is .of the follower type, consistsprimarily of a lever 98 and of a double sensor 100 which is pivotable ona pin 102 fixed to one end of the lever 98. The other end of the lever98 is pivotable on another pin 104 attached to a clevis 106, part ofwhich is'slidable in a blind bore 108 provided'in the body parallel tothe bore 12. A longitudinal bore in the clevis connects the bore 108 tothe actuating chamber. A spring 110 biases the clevis 106 on to thecover 16 in a position such as that shown in the FIGURE.

The lever 98 cooperates with the push rod 30 by means of the followingarrangement.

As the FIGURE shows, a slot 112 is provided in the push rod 30 betweenthe extension 34 and the helical groove50. The slot 112 runslongitudinally and passes diametrically through the rod 30. A pivot 114mounted perpendicularly in the rod 30 contains a central groove toreceive the lever 98. To summarize, the lever is introduced into theslot 112 and cooperates with the push rod 30 by way of a rotatableabutment 114. It should be'noted that in the embodiment described hereinand illustrated in the FIGURE the point of application A of the forcetransmitted by the push rod 30 is substantially halfway between the twopivot axes B, C of the pins 104, 102. Also, as explained in detailbelow, the axis B is capable under some circumstances of moving along astraight line ZZ coplanar with the straight lines XX and YY', which arethe axes of the bores 12 and 14, the line YY being situated between theother two.

The double sensor 100, seen from the side in the FIG- URE. is Y-shapedwhen viewed along the line XX. The base of the Y is a rocker 116 whichcooperates by way of a cam-forming surface 118 with the bearing member60 of the movable assembly 54. The contour of the cam surface 118 issuch that the point of contact D between the bearing member 60 androcker 116 remains substantially on the axis XX during movements of themovable assembly. The two arms of the Y are formed by two other twinrockers 120 which pass round the push rod 30 and which cooperate by wayof camforming surfaces 122 with an annular shoulder 124 on the end ofthe piston 18. The contours of the cam surfaces 122 are such that theperpendicular projection (represented by a point E) of the points ofcontact between the cam surfaces 122 and piston in the plane of theFIGURE remains substantially on the axis YY'. This arrangement reducesvery substantially the radial components occurring in the transmissionof forces between the sensor 100, piston 18 and movable assembly Inconclusion, the actuating chamber 22 is connected by an orifice 126 toanother independent brake circuit in the vehicle. By way of example, theactuating chamber may communicate with the brake circuit for the rearwheel brakes whereas the orifice 26 communicates with the brake circuitfor the front wheel brakes of the vehicle. The-arrangement may of coursebe reversed or changed. Moreover, according to a variant (not shown) ofthe invention, a conventional tandem mastercylinder may be mounted onthe body 10 on the left in the FIGURE so that it can be operated by theservo pis ton.

I The servomotor described above Operates as follows.-

By depressing the brake pedal the driver moves the push. rod 30 to theleft in the FIGURE. The force exerted by the spring 110 is greater thanthat exerted by the springs 27 and 76, so that during assisted operationof the servomotor the pin 104 remains stationary relative to the body,in the position illustrated. Due to the action of the push rod 30 thelever 98 pivots about the point B. The piston 18 therefore movesslightly further into the bore 14, closing the tilting valve 24 andtaking up the play in the 'front brake'circuit associated with theoutlet 26. As soon as the pressure in the chamber 20 becomesappreciable, the end 124 of the piston 18 on which the rockers 120 ofthe sensor 100 abut becomes fixed relative to the body. The forcetransmitted by the lever 98 to the point C now causes therockers .120 topivot about the point E, and the'movable assembly 54 shifts to the leftin the FIGURE. Being resiliently connected by the spring 80, the valvesleeve 64 also moves to the left in the FIGURE, closing the port andopening the port 92. The pressure fluid flows into the supply chamber 68and then enters the actuating chamber by way of the bore 38, ports 46,cavity 28 and narrow passage 50. From the actuating chamber the fluidalso supplies the rear brake circuit associated with the orifice 126.The presence of the narrow passage 50 creates a pressure differencebetween the cavity 28 and actuating chamber 22 which will be discussedin detail below. Nevertheless the pressure rises in the actuatingchamber and urges thepiston to the left in the FIG- URE. The doublesensor now pivots anti-clockwise due to the effect of the spring 76, thecam surfaces 122 still bearing on the piston 18. The movable assembly 54therefore'moves to the right in the FIGURE until it reaches anequilibrium position in which the valve sleeve closes the inlet port 92and outlet port 90, and the point D moves slightly to the left in theFIGURE along the axis XX- In the embodiment illustrated, this movementis of the order of 1 mm. The pressure now prevailing in the chamber isan equilibrium pressure which, acting on the effective cross-section ofthe rod 30, generates a proportionate reaction force at the pedal.

pedal. Assuming that due tooperation of the brake pedal the point A hasmoved a distance L in the direction YY, the point C is therefore moved adistance of about 2 L parallel to this line (taking the circular arccentered on B as identical to its tangent WW). On the other hand, sincethe point D has remained substantially stationary relative to its idleposition (moving 1 mm to the left), the point E has shifted about 2 X 2L along the axis YY, as the lines XX and YY due to the design, aresymmetrical relative to the line WW.

To summarize, for a movement L of the push rod 30,

the movement of the piston is equal to K K X L, K

being the lever arm ratio BC/AB and K being the ratio of the distancefrom XX to YY to the distance from YY to WW. In the embodimentdescribed, K and K areequal to 2, but within the scope of the inventionthe respective positions of the bores 12, 14 and 108 and the dimensionsof the lever 98 and sensor 100 may be modified to give the stroke ratiodesired by the user.

Between the idle position and the equilibrium position there is atransitory phenomenon due to the presence of the narrow passage 50between the cavity 28 and actuating chamber 22. At the time ofthepressure rise in the actuating chamber the pressure differencedepends chiefly on the flow rate. The pressure in the cavity acts on theend of the piston 18 (by way of the damper 36) and on the push rod 30.The principal result is that'a reaction at the brake pedal will be feltby the driver as soon as the distributing valve opens. This is becausethe reaction at the pedal is a function of the static pressure acting onthe push rod and of the dynamic pressure created by the rate of flowthrough the narrow passage 50.

This feature is very useful, particularly inheavy vehicles in which asubstantial pressure rise in the brakes is obtainable only by means of alarge fluid volume. In servomotors which do not have this dynamicreaction, the reaction at the pedal appearsvery abruptly and is thefiercer, the further the driver has to press his brake It should also benoted that the pressure rise in the actuating chamber 22 is accompaniedby corresponding movement of the piston 18 towards the left in theFIGURE, and that since the effective stroke of the piston 18 is greaterthan that of the rod 30 '(four times in the present example), some orall of thehelical groove 50 will emerge from the bore 52. The effectivecrosssection of the narrow passage therefore increases with the advanceof the piston, so that the pressure rise in the chamber 22 is not muchdelayed. Also, in the em bodiment illustrated, when the piston stroke islong enough (i.e., at the end of a braking period) the collar 42 coversthe mouth of the bore 14. The dimensions of these various components areof course specially adapted to the type of vehicle for which abrakeassisting servomotor embodying the invention is 'intended.

Furthermore, as indicated above, the pressure difference. acts on thedamper 36 as long as the dynamic pressure exists. The piston 18 willtherefore be urged to the left of the FIGURE before the pressure in thechamber 22 is appreciable. As a result the closing motion of thedistributing valve will be brought forward.

'Operation of the servomotor is then very smooth.

It should also be noted that operation of the brake circuit associatedwith the orifice 126 is later than that of the circuit connected to theoutlet 26. This latter fea- A failure of assisted braking is due chieflyto the fol-- lowing two causes: jamming of the valve sleeve in its bore,and loss of pressure at the inlet 88 due to failure of the pressuresource.

If the valve sleeve 64 jams in the bore at the start of or duringbraking, the force transmitted by the rocker 116 moves the bearingmember 58 off the sleeve 64. Also, due to the combination of the forcetransmitted by the push rod 30 with the resilience of the springs 76 and80 (now compressed), the'clevis 106 is urged into the borel08,'compressing the spring 110. The pin 104 moves to the left in theFIGURE along the axis ZZ.

The push rod 30 comes in contact with the damper 36 i and so operatesthe piston 18, without any risk of damaging the valve or followermechanism.

To prevent assisted braking from being resumed abruptly due to suddenfreeing of the valve sleeve, the bearing member 60 is capable of closingthe port during unassisted operation of the piston 18. When the driverreleases the brake pedal, of course, the various components of theservomotor return to the idle positions shown in the FIGURE, so thatassisted braking is available next time the driver brakes. v

In the event of a hydraulic failure, unassisted operation takes placeexactly aspreviously described. Wh en the piston 18 is operated directlyby the push rod 30, the ratio between the corresponding movements ofthese two components is equal to unity. The ratio of the push rod stroketo the piston stroke, which is one quarter during normal assistedoperation of the servomotor described, therefore increases for unasistedoperation.

Among other advantages of the distributing valve described above, it ispressure-balanced and therefore does not react appreciably on the rocker116.- Also, only the valve sleeve requires very accurate machining, asslight leakage between the bearing members 58, 60 and the surface of thebore 66 is acceptable (and makes the risk of jamming of the movableassembly very small).

The invention is not restricted to the embodiment described, and inparticula'r it covers variants (not shown) having any of the followingfeatures.

The narrow passage 50 is omitted, and the supply to the actuatingchamber 22 is made by way of the bore 108, which is connected directlyto the chamber 68. The clevis 106 may also act as a safety valve in thesame way as the bearing member 60 in the event of a failure of assistedoperation due to jamming of the dis tributing valve.

I claim:

1. In a hydraulic power control device:

a housing defining an actuating chamber therewithin;

a servopiston slidably mounted in said housing and responsive to thefluid pressure level in said actuating chamber;

a distributor valve in said housing controlling communication betweensaid actuating chamber and a fluid pressure source;

an input rod linearly and slidably mounted in said housing for actuatingsaid distributor valve, said input rod including means for engaging saidservo piston for manual movement'of the latter upon failure of saidfluid pressure source; and

a follower mechanism for interconnecting said distributor valve, saidpush rod, and said servo piston, said follower mechanism including asensor having a pair of arms, one of said arms cooperatingwith saidservo piston, the other arm cooperating with said distributor valve, alever, means pivotally mounting one end of said lever on said housing,and means pivotally mounting the other end of the lever on said sensor,said input rod including abutment means for engagement with said lever.2. The invention of claim 1: said means pivotally mounting said one endof the lever on said housing including a pin, means mounting said pinfor sliding movement with respect to said housing, and resilient meansyieldably urging said pin towards a predetermined position with respectto said 8 housing.

3. The invention of claim 2:

said sensor having cam forming surfaces on each of said arms cooperatingrespectively with said servo piston and with the distributing valve,said means mounting the other end of the lever to the sensor beinglocated between said cam forming surfaces.

4. The invention of claim 1:

said abutment means engaging said lever at a point substantially halfwaybetween the opposite ends thereof.

5. The invention of claim 1:

said push rod and said servo piston being substantially coaxial.

1. In a hydraulic power control device: a housing defining an actuating chamber therewithin; a servo piston slidably mounted in said housing and responsive to the fluid pressure level in said actuating chamber; a distributor valve in said housing controlling communication between said actuating chamber and a fluid pressure source; an input rod linearly and slidably mounted in said housing for actuating said distributor valve, said input rod including means for engaging said servo piston for manual movement of the latter upon failure of said fluid pressure source; and a follower mechanism for interconnecting said distributor valve, said push rod, and said servo piston, said follower mechanism including a sensor having a pair of arms, one of said arms cooperating with said servo piston, the other arm cooperating with said distributor valve, a lever, means pivotally mounting one end of said lever on said housing, and means pivotally mounting the other end of the lever on said sensor, said input rod including abutment means for engagement with said lever.
 2. The invention of claim 1: said means pivotally mounting said one end of the lever on said housing including a pin, means mounting said pin for sliding movement with respect to said housing, and resilient means yieldably urging said pin towards a predetermined position with respect to said housing.
 3. The invention of claim 2: said sensor having cam forming surfaces on each of said arms cooperating respectively with said servo piston and with the distributing valve, said means mounting the other end of the lever to the sensor being located between said cam forming surfaces.
 4. The invention of claim 1: said abutment means engaging said lever at a point substantially halfway between the opposite ends thereof.
 5. The invention of claim 1: said push rod and said servo piston being substantially coaxial. 